In a system to retrieve a map by using a speech command such as a car-navigation system, a user often speaks a name of place or institution in an area of retrieval object. In the car-navigation system, a plurality of road-maps are previously stored in a map-database. The user's utterance word speech is recognized as a place name or an institution name. A map in which the place name or the institution name is included is retrieved from the map-database and presented to the user. In this case, if a point of the place name or the institution name as the recognition result is far from an area on the map, a possibility that the user's input speech is erroneously recognized is high. Accordingly, if the system unconditionally executes an operation for this erroneous recognition result, the error operation is often occurred as a result. For example, if a map including a point of the erroneous recognition result is retrieved from the map-database and presented to the user during driving a car, this presentation is useless for the user's driving.
Therefore, as a present method in the car-navigation system to retrieve a map in response to a speech command, a large number of place names described in the map-database are hierarchically arranged from high-level to low level such as state, city, town, street.
The user speaks place names from a high level to a low level in order. In short, while the user speaks the place names from the high level to the low level, the map of retrieval object is further limited as the small area in the map-database. However, assume that the user speaks a name place of a high level and the area of retrieval object is limited to some extent. In the next step, the place name of the user's input utterance is limited to place names included in the area of retrieval object. In this case, if the user wishes to input a place name outside the area of retrieval object, this input processing of the system is returned to the highest level (for example, state) and the user must input the place name of the highest level (state name) again. This operation is troublesome for the user.
In this way, in the car-navigation system to retrieve a map by the user's input speech command, the large number of place names in the maps are hierarchically arranged and the map of the retrieval area is limited by the place name of the user's utterance from high level to low level. However, in this condition that the map of the retrieval area is limited to some extent, if the user utters a place name outside the retrieval area in order to retrieve another map, the user must release this limitation of the retrieval area in the system and the user must utter a place name of the highest level again. This operation is very troublesome for the user.